As the childs father, he has just as much a right to his childs medical records as the mother does. Unless there is a court order barring him from seeing the medical records, it's against the law for any doctor, hospital or clinic to deny him those records.
This is the statute for OK
§10-5.2. <
http://www2.lsb.state.ok.us/os/os_10-5.2.rtf> Certain information and records to be available to both custodial and noncustodial parent.
Any information or any record relating to a minor child which is available to the custodial parent of the child, upon request, shall also be provided the noncustodial parent of the child. Provided, however, that this right may be restricted by the court, upon application, if such action is deemed necessary in the best interests of the child. For the purpose of this section, "information" and "record" shall include, but not be limited to, information and records kept by the school, physician and medical facility of the minor child.
Also, copy and paste this URL into your browser. This is a letter to send to any doctor or hospital who tries to deny your brother access to his childs records.
http://www.deltabravo.net/custody/medrecords.htm